In some engines, an electronically controlled throttle is used for improved performance. In addition, engines also may be controlled using engine output, or torque control where the actual engine torque is controlled to a desired engine torque through an output adjusting device, such as with the electronic throttle, ignition timing, air-fuel ratio, or various other devices.
One method to monitor engine control systems determines if actual engine torque is greater than desired engine torque. Actual engine torque is determined in accordance with engine airflow and/or injected fuel amount, and various other factors. Such a method is described U.S. Pat. No. 5,692,472.
The inventors herein have recognized a disadvantage of the above approach. In particular, when such a method is utilized with vehicles having multiple torque sources, such as hybrid electric vehicles, several different torque values can be considered. For example, torque produced by an electric motor and torque produced by an internal combustion engine can both contribute to overall drive torque. Thus, additional variables may be used to account for various torque sources. Each of these additional variables can then have redundancy. In the end, monitoring using the above structure may result in additional cost and/or complexity.